Batwing LED with Remote Phosphor Configuration

ABSTRACT

A semiconductor structure includes a module with a plurality of die regions, a plurality of light-emitting devices disposed upon the substrate so that each of the die regions includes one of the light-emitting devices, and a lens board over the module and adhered to the substrate with glue. The lens board includes a plurality of microlenses each corresponding to one of the die regions, and at each one of the die regions the glue provides an air-tight encapsulation of one of the light-emitting devices by a respective one of the microlenses. Further, phosphor is included as a part of the lens board.

PRIORITY DATA

This application is a continuation application of U.S. patentapplication Ser. No. 13/114,730, filed on May 24, 2011, entitled“BATWING LED WITH REMOTE PHOSPHOR CONFIGURATION,” now U.S. Pat. No.8,497,519, the disclosure of which is hereby incorporated by referencein its entirety.

FIELD OF THE INVENTION

The present disclosure relates generally to a semiconductor device and,more particularly, to semiconductor lighting emitting diode (LED).

BACKGROUND

A Light-Emitting Diode (LED), as used herein, is a semiconductor lightsource for generating a light at a specified wavelength or a range ofwavelengths. LEDs are traditionally used for indicator lamps, and areincreasingly used for displays. An LED emits light when a voltage isapplied across a p-n junction formed by oppositely doping semiconductorcompound layers. Different wavelengths of light can be generated usingdifferent materials by varying the bandgaps of the semiconductor layersand by fabricating an active layer within the p-n junction.

Traditionally, LEDs are made by growing light-emitting structures on agrowth substrate. The light-emitting structures along with theunderlying growth substrate are separated into individual LED dies. Atsome point before or after the separation, electrodes or conductive padsare added to the each of the LED dies to allow the conduction ofelectricity through the structure. LED dies are then packaged by addinga package substrate, optional phosphor material, and optics such as lensand reflectors to become an optical emitter.

Optical emitter specifications typically identify application-specificradiation patterns outputted by the optical emitter. A commonly usedbeam pattern is the batwing beam pattern for illuminating a flatsurface, in traffic signal applications, or in a backlighting unit for adisplay. The batwing beam pattern may be defined by having two roughlyequal peaks in a candela distribution plot with a valley between thepeaks at about 0 degrees.

Optical emitters are designed to meet these specifications. Whileexisting designs of optical emitters have been able to meet batwing beampattern requirements, they have not been entirely satisfactory in everyaspect. Reliable and more efficient designs that are easier tomanufacture continue to be sought.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method of fabricating an opticalemitter according to various aspects of the present disclosure.

FIGS. 2A to 2F illustrate cross-sectional views of an optical emitter atvarious stages of fabrication according to various embodiments.

FIGS. 3A to 3C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

FIGS. 4A to 4C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

FIGS. 5A to 5C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

SUMMARY

One aspect of the present disclosure involves an optical emitterincluding one or more Light-Emitting Diode (LED) dies, a packagesubstrate attached to one side of the one or more LED dies, electricalconnections between the one or more LED dies and terminals on thepackage substrate, a molded lens bonded to the package substratedirectly contacting the one or more LED dies and phosphor materialembedded in the molded lens in a circumferential cylinder. The opticalemitter outputs a batwing beam pattern through the molded lens.

Another aspect of the present disclosure involves a method offabricating an optical emitter. The method includes attaching one ormore Light-Emitting Diode (LED) dies to a package substrate,electrically connecting the one or more LED dies and terminals on thepackage substrate, molding a lens over the package substrate and the oneor more LED dies, wherein the lens includes a circumferential trench,and filling the circumferential trench with a phosphor material. A topsurface or a portion of the top surface of the molded lens may be coatedwith a high reflectivity material.

The circumferential trench and the subsequent circumferential phosphorcylinder may have uniform or varying circumference. A portion of thecylinder wall may be thicker than another portion. The walls may besloped inwards linearly or in a curved manner. The molded lens alongwith the optional high reflective surface reflect light emitted by theone or more LED dies sideways through the circumferential phosphorcylinder.

These and other features of the present disclosure are discussed belowwith reference to the associated drawings.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of variousembodiments. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a feature over or on another feature in thedescription that follows may include embodiments in which the featureand the another feature are formed in direct contact, and may alsoinclude embodiments in which additional features may be formed betweenthe feature and the other features, such that the features may not be indirect contact. Of course, the description may specifically statewhether the features are directly in contact with each other. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Generally, an LED package, also referred to herein as an opticalemitter, includes an LED die attached to a package substrate, a layer ofphosphor material, and some optical components such as lenses and/orreflectors. The LED die is electrically connected to circuitry on thepackage substrate in a number of ways. One connection method known tothe inventors involves attaching the growth substrate portion of the dieto the package substrate, and forming electrode pads that are connectedto the p-type semiconductor layer and the n-type semiconductor layer inthe light-emitting structure on the die, and then bond wiring from theelectrode pads to contact pads on the package substrate. Anotherconnection method involves inverting the LED die and using solder bumpsto connect the electrode pads on the light-emitting structure directlyto the package substrate. This is known as a flip-chip package. Yetanother connection method involves using hybrid connectors. Onesemiconductor layer, for example the p-type layer, may be wired bondedto the package substrate while the other layer (n-type layer) may besoldered or metal bonded to the package substrate after removing thegrowth substrate.

The LED package may include one or more phosphor materials that areusually applied directly onto the LED die. Conventional methods ofapplying the one or more phosphor materials include spray-coating thephosphor materials in a concentrated viscous fluid medium, for example,liquid glue, onto the surface of the LED die through which the generatedlight must pass. As the viscous fluid sets or cures, the phosphormaterial becomes a part of the LED package. However, dosage anduniformity of a sprayed-on phosphor material is difficult to control.Further, the phosphor material is disposed in close proximity to the LEDdie and subjected to thermal cycling, which degrades the phosphormaterial over time reducing light output and changing color output.

Optical components such as reflectors and lenses are used to shape theradiation pattern, or beam pattern. Several optical components are oftenused to achieve a desired pattern, for example, a batwing beam pattern.A lens may be made of plastic, epoxy, or silicone and is attached to thepackage substrate by gluing its edge onto the package substrate.Usually, the lens is manufactured separately from the LED die and isavailable in specific sizes and shapes.

Conventional batwing optical emitters use two lenses to achieve thebatwing pattern. A first lens, or primary optics, is a transparent lensattached directly or formed directly on the LED die. The first lens isusually a semi-ellipsoid and functions primarily to extract as muchlight as possible from the LED die. A second lens, or secondary optics,is fitted and attached over the first lens and serves to shape the beampattern. Thus, using the methods known to the inventors, a variety ofbeam patterns may be generated by changing the second lens designwithout changing other portions of the LED package. Light thus generatedby the LED die may travel through a sapphire growth substrate, one ormore layers of phosphor material, through a first lens, possibly a gapbetween the first and the second lens, and finally through the secondlens for shaping the batwing pattern. The multiple interfaces can eachreduce the light output a small amount, and together, the light outputis reduced significantly from that of the LED dies.

The batwing optical emitter known to the inventor using the combinationof a primary and secondary optics suffers from several issues withmanufacturing, cost, and design. Because the second lens is madeseparately from the rest of the LED package, it is fitted over the firstlens during assembly. Alignment of these optical components affects theresulting beam pattern and thus the tolerance for the alignment is verylow. The low tolerance presents manufacturing issues and affects yield.Cost of the batwing optical emitter includes two lenses, which rendersthe batwing optical emitter more expensive than other optical emittersthat generate other beam patterns. As the LED dies becomes moreefficient and its dimensions reduce, the separately made second lens andthe alignment issue makes dimension reduction of the overall LED packagedifficult. While smaller second lens can be made, a smaller lensmagnifies mis-alignment issues and presents handling difficulties duringfinal assembly. Furthermore, the proximity of the phosphor to the LEDdies reduces device reliability and changes color over time.

An optical emitter in accordance with the present disclosure involvesonly one lens molded directly on one or more LED dies with the phosphormaterial not directly over the LED dies. Illustrated in FIG. 1 is aflowchart of a method 101 for fabricating an optical emitter inaccordance with various embodiments of the present disclosure. FIGS. 2Ato 2F are diagrammatic fragmentary cross-sectional side views of theoptical emitter during various fabrication stages in accordance with oneembodiment of the method 101 in FIG. 1. The optical emitter may be astandalone device or a part of an integrated circuit (IC) chip or systemon chip (SoC) that may include various passive and activemicroelectronic devices such as resistors, capacitors, inductors,diodes, metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJTs), laterally diffused MOS (LDMOS) transistors,high power MOS transistors, or other types of transistors. It isunderstood that FIGS. 2A to 2F have been simplified for a betterunderstanding of the inventive concepts of the present disclosure.Accordingly, it should be noted that additional processes may beprovided before, during, and after the method 101 of FIG. 1, and thatsome other processes may only be briefly described herein.

Referring to FIG. 1, the method 101 begins with block 103 in which oneor more Light-Emitting Diode (LED) dies are attached to a packagesubstrate. FIG. 2 shows a cross-sectional view of a package substrate201. The package substrate 201 is a silicon substrate, a ceramicsubstrate, a gallium nitride substrate, a metal core printed circuitboard (MCPCB) or other package substrates used for packaging LEDs. Thepackage substrate may include metal pads 203 and through substrate vias205. Metal pads 203 and through substrate vias (TSVs) 205 are used onpackaging substrates in wafer level packaging to conduct electricityand/or heat. Though not necessary for the embodiments described in thisdisclosure, the use of metal pads and through substrate vias on asilicon substrate improves thermal and electrical conductivities.

FIG. 2B illustrates the LED dies 211 attached to the package substrate201. In certain embodiments, where the growth substrate side of the LEDdie is attached to the package substrate, the attachment may beperformed by simply gluing the LED die using any suitable conductive ornon-conductive glue, depending on whether the side of the LED die andthe package substrate to be attached are conductive and whetherisolation is required. In embodiments where the LED die side opposite ofthe growth substrate is attached to the package substrate, theattachment may include electrically connecting the LED die by bondingthe electrode pads on the LED to contact pads on the package substrate.This bonding may involve soldering or other metal bonding. In someembodiments, the growth substrate is removed and one side of the LED dieis bonded and electrically connected to the substrate. In this case theattaching may be accomplished using metal bonding such as eutecticbonding.

In one example, the LED dies are attached to the die by soldering. Tobond the LED die by soldering, a solder is printed on the packagesubstrate and reflowed while contacting the LED die. In another example,the LED dies are attached by being glued to the substrate using athermally conductive glue.

An LED die 211 includes a light-emitting structure (not shown) and oneor more electrode pads for electrically connecting to a packagesubstrate, the details of which are not shown in FIG. 2B. While thefollowing disclosure refers to an optical emitter with a blue LED, theconcepts describes herein could apply to other color LEDs as long as aphosphor is used to convert at least a portion of the light emitted fromthe LED to a different wavelength. The light-emitting structure has twodoped layers and a multiple quantum well layer between the doped layers.The doped layers are oppositely doped semiconductor layers. In someembodiments, a first doped layer includes an n-type gallium nitridematerial, and the second doped layer includes a p-type material. Inother embodiments, the first doped layer includes a p-type galliumnitride material, and the second doped layer includes an n-type galliumnitride material. The MQW layer includes alternating (or periodic)layers of active material, for example, gallium nitride and indiumgallium nitride. For example, in one embodiment, the MQW layer includesten layers of gallium nitride and ten layers of indium gallium nitride,where an indium gallium nitride layer is formed on a gallium nitridelayer, and another gallium nitride layer is formed on the indium galliumnitride layer, and so on and so forth.

The doped layers and the MQW layer are all formed by epitaxial growthprocesses. After the completion of the epitaxial growth process, a p-njunction (or a p-n diode) is essentially formed. When an electricalvoltage is applied between the doped layers, an electrical current flowsthrough the light-emitting structure, and the MQW layer emits light. Thecolor of the light emitted by the MQW layer associated with thewavelength of the emitted radiation, which may be tuned by varying thecomposition and structure of the materials that make up the MQW layer.The light-emitting structure may optionally include additional layerssuch as a buffer layer between the substrate and the first doped layer,a reflective layer, and an ohmic contact layer. A suitable buffer layermay be made of an undoped material of the first doped layer or othersimilar material. A light-reflecting layer may be a metal, such asaluminum, copper, titanium, silver, alloys of these, or combinationsthereof. An ohmic contact layer may be an indium tin oxide (ITO) layer,a titanium nitride layer, or a thin layer of other conductive materialthat is substantially transparent to the light emitted by the LED. Thelight reflecting layer and ohmic contact layer may be formed by aphysical vapor deposition (PVD) process, a chemical vapor deposition(CVD), or other deposition processes.

After the LED die is attached to the substrate, the LED die iselectrically connected to the package substrate in operation 105 ofFIG. 1. At least two electrical connections are made, one each to thep-type and n-type doped layers. In some cases, two electricalconnections are made to the p-type layer for current spreading purposes.As discussed, the electrical connection may involve wire bonding,soldering, metal bonding, or a combination of these. FIG. 2B furtherillustrates wire bonds 213 between the LED dies 211 and metal pads 203.The wire bonds 213 connect electrodes on the LEDs the metal pads 203,which is electrically connected to terminals on the back side of thepackage substrate 201 through the TSVs 205. Although the FIG. 2Billustrate a horizontal package, the LED dies may be attached to thepackage substrate in a number of ways, including vertical packagingusing only one wire bond or flip chip packaging using no wires. Becausethe electrical connection 213 may take a variety of forms, the structureshown in FIG. 2B is illustrative only—the electrical connections 213need not be a wire bond.

Referring back to FIG. 1, at operation 107 a lens is molded over the LEDdies and the package substrate. The lens includes a circumferentialtrench. The lens may be formed by injection molding or compressionmolding. A variety of materials may be used as the lens. Suitablematerials have a high optical permissivity (transparency), a viscositysuitable for molding, appropriate adhesion to the package substrate, andgood thermal conductivity and stability (i.e., do not degrade or changecolor during thermal cycling). Example materials include silicone,epoxy, certain polymers, resins and plastics including Poly(methylmethacrylate) (PMMA). Suitable materials are flowable for molding intothe lens and can be cured into a defined shape. Some suitable materialsmay have thermal expansion coefficients that are similar to that of thepackage substrate and/or can absorb stress caused by a difference in thethermal expansion during thermal cycling. Examples of suitable lensmaterials include Shin-Etsu's line of SCR and KER silicone resins andrubber materials and Dow Cornings' various lines of silicon gels,elastomers, and silicone resins. As understood, a manufacturer in theindustry can adjust the refractive index of the lens material as acustomer specifies. Thus, one skilled in the art can select a suitablelens material based on suitable material properties other than therefractive index first, then specify the refractive index within a rangethat can be supplied by the manufacturer.

In certain embodiments, a compression molding method is used as shown inFIG. 2C. A lens precursor material 221 is dispensed over the LED diesand the package substrate and then a lens mold 223 is placed over lensprecursor material 221. The lens mold 223 includes circumferentialtrench 225 and may include one or more openings for excess lens materialand air to escape the mold 223 as the mold 223 is compressed against thepackage substrate. The position and number of openings on the lens mold223 depends on the process conditions and the material propertiesinvolved. A number of openings may be used and the openings may belocated at different places. While FIG. 2C illustrate one lens cavityplaced over two LED dies, the lens mold may include multiple moldcavities that would fit over a package substrate having many LED diesattached thereon to form lenses for a number of packages at the sametime. The package substrate 201 may include alignment marks betweenindividual LED dies to ensure that the lens cavities are placedaccurately over the LED dies.

To ensure a good fill, the gas inside the lens cavity may be evacuatedthrough one or more openings. Alternatively, this operation is performedin a vacuum environment, in which the instant openings may be notrequired. The lens precursor material/glue 221 may be heated or underpressure. The lens precursor material 221 fills the lens cavity to formthe lens when the mold 223 is pressed against the package substrate.

The lens precursor material is cured to set so that it retains its shapeand adheres to the package substrate and LED die as shown. Radiation orother energy may be applied to the lens mold, which allows the radiationthe pass through. The radiation may be an ultraviolet (UV) radiation,thermal radiation (infrared), microwave, or another radiation that cancure the lens glue. Glue materials that cure under UV light or underheat application are commercially available. In some instances, curingmay be accomplished by only thermal energy, which need not be applied inthe form of radiation. Conductive heat energy may be applied through thepackage substrate 201 or through heating of the lens mold 223.

After the lens has cured, the lens mold may be removed, as shown in FIG.2D. The lens mold 223 is removed so as not to remove the lens 231 fromthe package substrate 201. In one embodiment, some gas can be added viaone or all of the mold openings to help separate the lens 231 from thelens mold 223. Other techniques include changing the temperature ofeither the molded lens or the lens mold such that a temperaturedifference exists or using a removal template in the lens mold 223. Inanother embodiment, the circumferential trenches are made to havedifferent trench widths. The trench may be narrower at the bottom andwider at the top so that the lens mold is easier to remove.

The circumferential trench 233 is thus formed in the lens 231. Note thatFIG. 2D shows neighboring circumferential trenches 235 and 237 formed bythe same mold. These neighboring circumferential trenches 235 and 237belong to neighboring optical emitters. Eventually, the packagesubstrate will be diced into individual optical emitters at the locationbetween the circumferential trenches, for example, between trenches 233and 237, through the lens material to form individual optical emitters.

Referring back to FIG. 1, in operation 109 the circumferential trenchesare filled with a phosphor material. The phosphor material may be filledby dispensing or injecting the phosphor material into thecircumferential trenches, as shown in FIG. 2E. The dispensing may beaccomplished by printing a viscous liquid containing the phosphor overthe lens material, and flowing the liquid into the trenches byvibration, either via physical movement of the package substrate orsonic/ultrasonic waves. The dispensing may also be accomplished bysubmerging the entire partially fabricated package into a liquid mediumcontaining the phosphor material. The injecting may be accomplished bytracing the trench with an injection gun or pen. An entirecircumferential trench may be injected by using injection guns withoutput ports having the same shape as the circumferential trench.Further, the circumferential trenches may be filled by a spin coatingprocess where excess material is spun off the surface of the lens. Oneskilled in the art would be able to select the right material withphosphor to form the phosphor material so that the trenches can beproperly filled based on the filling technique to be used.

After the phosphor material is applied to the circumferential trench, itis solidified into a circumferential cylinder, shown as 241 in FIG. 2E.Phosphor may be mixed with silicone, epoxy, polymers, resins, siliconeresin and plastics including Poly(methyl methacrylate) (PMMA). Thematerial is preferably selected to have similar thermal expansioncoefficients as the lens so as to minimize thermal cycling inducedstress between the two materials. Of course, the same base material maybe used—the only difference being the addition of phosphor. Depending onthe material properties of the mixture, the phosphor material may besolidified by curing with radiation or heat and by setting and allowingchemical reactions to form a matrix. The phosphor cylinder is thenembedded in the lens.

If the circumferential trench has varying widths, then thecircumferential cylinder formed also has varying thicknesses. This wallof phosphor serves to change the wavelength of LED emitted light andreflected light so that a light of different color from what was emittedis perceived outside of the optical emitter. The thickness variance maydepend on the expected light at different locations of the cylinder tocreate a uniform color distribution. For example, where more reflectedlight is expected, the cylinder wall may be thicker so the lightconverted by the phosphor remains the same ratio regardless of the angleof perception. This phosphor cylinder 241 may also be used inconjunction with another phosphor layer, for example, another phosphorcylinder concentric to the first one (243 and 245) or a phosphor layerapplied directly to the LED dies to create a variety of colors, forexample, white light. To create white light, when only one phosphorcylinder is used, the phosphor may be a phosphor that generates yellowlight when excited by a blue light. When two phosphor layers are used,one phosphor layer may be a green phosphor and another may be a redphosphor. In other embodiments, phosphor cylinders 243 and 245 areseparate cylinders belonging to different optical emitters.

In some embodiments, the curing for the phosphor cylinder and the lensmay occur sequentially or together. The lens may be formed and set witha soft cure so as to retain its shape. Then the phosphor material may beadded to the circumferential trench. The two materials may be curedtogether in a “hard bake” to finalize the solidification process.

In other embodiments, the lens may be formed and cured completely beforethe phosphor material is added. The phosphor cylinder may be designed tobe softer than the lens material. Then during the thermal cycling thephosphor cylinder may absorb some of the thermal expansion stresseswhich reduces the chance that the thermal cycling stresses delaminatesthe lens from the package substrate.

Referring back to FIG. 1, after the lens and the phosphor cylinder areformed, a top surface of the lens may be optionally coated with areflective material in operation 111. As noted above, the requiredreflectivity of the surface coating material depends on the batwing beampattern requirements and a variety of coating material may be used. Thesurface coating material may be dispensed, sprayed, spun, or otherwisedeposited on the lens top surface. An example would be to use a gelcontaining reflective additives, for example, a silicon gel, dispensedonto the top surface of the lens. Additives may include metal particlessuch as silver or other metals, some metal oxide such as titanium oxide,zinc oxide, and zirconium oxide. Other highly reflective additives maybe used. Examples of other highly reflective coatings include dielectricfilms tuned to reflect the specific wavelengths of light emitted by theLED die. In some embodiments, the surface coating selected reflects morethan 80% of the incident light, about 90% of the incident light, or morethan 90% of the incident light. In some instances the surface coatingmerely coats a portion of top surface. In other instances the surfacecoating may coat the entire top surface. FIG. 2F illustrate a reflector251 coating on a portion of the lens.

In other embodiments, the reflective coating is not used. The lens maybe shaped such that light reaching the top surface from the LED die ismostly reflected off the surface as total internal reflection (TIR). TIRis an optical phenomenon that occurs when a ray of light strikes aboundary between two medium at an angle larger than a particularcritical angle with respect to the normal to the surface. At this largerangle, if the refractive index is lower on the other side of theboundary, no light can pass through and all of the light is reflected.The critical angle is the angle of incidence above which the totalinternal reflection occurs. If the angle of incidence is greater (i.e.,the ray is closer to being parallel to the boundary) than the criticalangle—the angle of incidence at which light is refracted such that ittravels along the boundary—then the light will stop crossing theboundary altogether and instead be totally reflected back internally.The top lens surface in accordance with various embodiments of thepresent disclosure has a surface that renders most of the angle ofincidence greater than the critical angle. Because the refractive indexon the other side of the top surface is lower (for example, air has arefractive index of about 1) than that of the lens (for example, siliconmolding has refractive indices of about 1.4 to 1.55), most of the lightfrom the LED may be reflected as TIR. A combination of surface coatingand lens shape design may be used to ensure that most of the lightemitted by the LED dies is reflected from the top surface.

Referring back to FIG. 1, the package substrate may be diced into anumber of optical emitters in operation 113. As shown in FIG. 2F, theoptical emitter is separated from its neighbors outside of the phosphorcylinder. The package substrate may be diced using mechanical means suchas sawing or cutting. The package substrate may also be diced usingradiation energy, such as laser. The use of laser allows a non-linearcut to be used. For example, the optical emitters may have a round baseinstead of a rectangular base.

The optical emitter according to various embodiments of the presentdisclosure applies to having only one LED die as well as several LEDdies. The LED dies may be arranged in a linear array, in a rectangulararray, or in a circle or other shapes. FIGS. 3A to 3C illustrate anumber of embodiments. FIG. 3A is a cross section view of FIG. 3B or 3C,at a 45 degree angle through a center of the optical emitter. Theembodiments of FIGS. 3A to 3C include no reflective coating on the topsurface of the lens 301. In these embodiments, four LED dies 303 aremounted on the substrate 305. In FIG. 3B, each die has a side closest tothe center of the optical emitter. In FIG. 3C, each die has a cornerclosest to the center of the optical emitter. The placement of the diesdepends on the profile of the lens to cause TIR. Note that the packagesubstrate for the optical emitter may be a rectangle or square as shownin FIG. 3B; or round or oval as shown in FIG. 3C. The phosphorcircumferential cylinder 311 may also be round or oval depending on theshape and placement of the LED dies and the lens shape. In a top view,the lens has a circular or oval shape. The shape may be achieved by themold when the lens is formed. The shape may also be formed by subsequentcutting or etching.

FIGS. 4A to 4C illustrate a number of other embodiments. FIG. 4A is across section view of FIG. 4B or 4C, at a 45 degree angle through acenter of the optical emitter. The embodiments of FIGS. 4A to 4Cincludes reflective coating on a portion of the top surface of the lens401. The portion may be a center portion. The coating may partially filla cavity as shown in FIG. 4A, or may be applied as a thin layer. Inthese embodiments, four LED dies 403 are mounted on the substrate 405.In FIG. 4B, each die has a side closest to the center of the opticalemitter. In FIG. 4C, each die has a corner closest to the center of theoptical emitter. The reflective coating, the shape of the lens, andplacement of the dies together cause TIR off the top surface of thelens. Note that the package substrate for the optical emitter may be arectangle or square as shown in FIG. 4B; or round or oval as shown inFIG. 4C.

FIGS. 5A to 5C illustrate yet a number of other embodiments. FIG. 5A isa cross section view of FIG. 5B or 5C, at a 45 degree angle through acenter of the optical emitter. The embodiments of FIGS. 5A to 5C includereflective coating on a portion of the top surface of the lens 501. Theportion may be a center portion. The coating may fill a cavity as shownin FIG. 5A, or may be applied as a thin layer over the entire topsurface of the lens. In these embodiments, four LED dies 503 are mountedon the substrate 505. In FIG. 5B, each die has a side closest to thecenter of the optical emitter. In FIG. 5C, each die has a corner closestto the center of the optical emitter. The reflective coating causes TIRoff the top surface of all of the lights generated by the LED dies toexit the optical emitter from the sides. Note that the package substratefor the optical emitter may be a rectangle or square as shown in FIG.5B; or round or oval as shown in FIG. 5C.

In other embodiments of the present disclosure, a different number ofLED dies are used. For example, three LED dies may be arranged to formvertices of an equilateral triangle. In another embodiment, five LEDdies are arranged to form two rows—one row of two LED dies and one rowof three LED dies. In each of these multiple LED die configurations, onelens is formed over the LED dies.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein. Itis understood, however, that these advantages are not meant to belimiting, and that other embodiments may offer other advantages. Thoseskilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating an optical emitter,comprising: attaching one or more Light-Emitting Diode (LED) dies to apackage substrate; electrically connecting the one or more LED dies andterminals on the package substrate; molding a lens over the packagesubstrate and the one or more LED dies, wherein the lens includes acircumferential trench; and, filling the circumferential trench with afirst phosphor material.
 2. The method of claim 1, further comprisingcoating a top surface of the molded lens with a high reflectivitymaterial.
 3. The method of claim 1, wherein the molding a lens over thepackage substrate and the LED die comprises: placing a lens mold overthe package substrate and the one or more LED dies; inserting a lensglue into the lens mold; curing a molded lens.
 4. The method of claim 3,wherein the inserting a lens glue includes evacuating a space inside thelens mold.
 5. The method of claim 1, wherein the filling thecircumferential trench with a phosphor material comprises injecting aphosphor and glue mixture and solidifying the phosphor and glue mixture.6. The method of claim 1, further comprising dicing the packagesubstrate into a plurality of optical emitters.
 7. The method of claim1, wherein electrically connecting the one or more LED dies and thepackage substrate comprises connecting more than one LED dies in seriesand connecting end LED dies to terminals on the package substrate. 8.The method of claim 1, further comprising forming a phosphor componentusing a second phosphor material different than the first phosphormaterial.
 9. A method of fabricating an optical emitter, comprising:disposing a plurality of Light-Emitting Diode (LED) dies on a packagesubstrate, the package substrate including a plurality of terminals;electrically coupling the LED dies to the terminals on the packagesubstrate; forming a lens over the package substrate, the lens coveringthe LED dies, the lens containing a trench; and filling the trench withphosphor.
 10. The method of claim 9, wherein the trench of the lens is acircumferential trench.
 11. The method of claim 9, further comprising:dispensing a reflective gel over the lens; and dicing the packagesubstrate into a plurality of optical emitters.
 12. The method of claim9, wherein the form the lens further comprises: placing a lens mold overthe package substrate and the LED dies, the lens mold including acavity; injecting a lens precursor material into the cavity of the lensmold; and thereafter curing the lens precursor material.
 13. The methodof claim 12, further comprising: before the injecting the lens glue,evacuating a gas inside the cavity of the lens mold.
 14. The method ofclaim 9, wherein the filling the trench comprises injecting a mixture ofphosphor particles and glue; and further comprising: solidifying themixture.
 15. The method of claim 9, wherein electrically couplingcomprises electrically coupling at least a subset of the LED dies inseries.
 16. A method of fabricating an optical emitter, comprising:disposing a plurality of Light-Emitting Diode (LED) dies on a packagesubstrate, the package substrate including a plurality of terminals;electrically coupling the LED dies to the terminals on the packagesubstrate, wherein at least a subset of the LED dies are electricallycoupled together in series; forming a lens over the package substratethrough a compression molding process, the lens covering the LED dies,the lens containing a trench; filling the trench with phosphor; andsingulating the LED dies.
 17. The method of claim 16, furthercomprising: dispensing a reflective gel over an upper surface of thelens.
 18. The method of claim 16, wherein the trench of the lens is acircumferential trench.
 19. The method of claim 16, wherein the form thelens further comprises: placing a lens mold over the package substrateand the LED dies, the lens mold including a cavity; evacuating a gasinside the cavity of the lens mold; injecting a lens precursor materialinto the cavity of the lens mold; and thereafter curing the lensprecursor material.
 20. The method of claim 16, wherein the filling thetrench comprises filling the trench with a mixture of phosphor particlesand glue; and further comprising: solidifying the mixture after themixture is filled into the trench.